This invention relates generally to optical reproducing apparatus and, more particularly, is directed to a device for rapidly moving an optical pick-up device of an optical reproducing apparatus to a desired position on a record disc during a search operation.
Apparatus is known in the art for optically reproducing an information signal from a record disc during rotation of the latter. With such apparatus, an optical pick-up device is positioned below the record disc and projects a laser beam onto the disc. The laser beam is modulated by, for example, audio information recorded on the disc in the form of small pits arranged in a spiral track or in concentric tracks, and the modulated laser beam is reflected from the underside of the disc back to the optical pick-up device which produces an output signal in response to the modulated laser beam and which supplies such signal to further processing circuitry for separating the audio information therefrom.
In one such apparatus, it has been proposed to detect address information also recorded on the record disc for performing a search or track jump operation so that reproduction at a desired position can be easily and quickly achieved. In particular, a selected address corresponding to the desired position is preset, and the pick-up device is rapidly moved across or transverse to the record tracks to the desired position on the record disc corresponding to the selected address.
In a small scale search or track jump operation in which the optical pick-up device is rapidly moved to a selected address which is located only a few tracks away from the track at which the pick-up device is presently located, the pick-up device can repeatedly be moved on a track by track basis. However, in a large scale search or track jump operation in which the selected track is relatively distant from the track at which the pick-up device is presently situated, the repeated track by track operation cannot practically be performed in a short period of time. As a result, one of the distinct advantages of a digital audio disc system, that is, rapid and easy movement of the pick-up device to a desired location, vanishes. Accordingly, for a large scale search operation, it is desirable to rapidly move or jump the pick-up device across a plurality of, for example, 10 or 100, record tracks at a time until the desired location is reached and, for a small scale search operation, to move the pick-up device in the aforementioned track by track movement.
For the large scale search operation, it has been proposed to supply a track jump signal to a drive device to control the latter to rapidly move or jump the device across a plurality of record tracks at a time until the desired location is reached. The track jump signal is comprised of a drive pulse signal which controls the drive device to move the optical pick-up device rapidly across a predetermined number of record tracks, followed by a brake pulse signal for controlling the drive device to brake movement of the optical pick-up device so that the pick-up device is accurately and quickly moved to the desired location. It is to be appreciated that, during the normal reproduction operation, a tracking error signal obtained in response to deviation of the reading position of the optical pick-up device from the center of the record track then being scanned is produced. This tracking error signal is supplied to the drive device which functions as a tracking servo control arrangement for moving the optical pick-up device in a direction transverse to each respective record track to correct for such deviation. However, during the search or track jump operation, the tracking error signal is not supplied to the drive device. Rather, in place thereof, the aforementioned track jump signal is supplied to the drive device, thereby rendering inoperative the tracking servo control operation.
As previously described, the track jump signal includes a drive pulse signal which results in a current of a first polarity flowing through a drive motor of the drive device to move the optical pick-up device rapidly across a predetermined number of record tracks. Thereafter, the brake pulse signal is supplied to the drive motor to cause a current of a second polarity opposite to the first polarity to flow through the drive motor to brake movement of the optical pick-up device to stop the latter at the desired location on the record disc. It is to be appreciated that the duration or period of each of the drive pulse signal and brake pulse signal is predetermined in accordance with the number of record tracks to be jumped over by the optical pick-up device during the search operation.
However, various problems result with such large scale search or track jump operation. In particular, the number of record tracks to be jumped or traversed by the optical pick-up device when a track jump signal is supplied to the drive device may differ depending upon the eccentricity of the disc, mechanical non-uniformity in the tracking control arrangement, temperature conditions and the like. As a result, it is difficult to ensure that the optical pick-up device is rapidly and accurately moved to jump over or traverse the record tracks to a desired location on the disc. In other words, the optical pick-up device may be moved past or overshoot the desired location as a result of an insufficient brake pulse signal or may not be moved completely to the desired location as a result of an excessive braking force caused by the brake pulse signal.